ffirs.indd

88 Speed Math for Kids
number, or three times, four times or even sixteen times the fi rst
reference number. In this case I would choose 40 as the second
reference number, as it equals 4 times 10.
We then write the reference numbers in parentheses to the side of
the problem, with the easy multiplier written fi rst and the second
number written as a multiple of the fi rst. So, we would write 10 and
40 as (10 × 4), the 10 being the main reference number and the 4
being a multiple of the main reference.
Th e problem is written like this:
(10 × 4) 8 × 37 =
Both numbers are below their reference numbers, so we draw the
circles below.
(10 × 4) 8 × 37 =
What do we write in the circles? How much below the reference
numbers are the numbers we are multiplying? Two and 3, so we
write 2 and 3 in the circles.
(10 × 4) 8 × 37 =
–2
–3
Here is the diff erence. We now multiply the 2 below the 8 by the
multiplication factor, 4, in the parentheses. Two times 4 is 8. Draw
another circle below the 8 (under the 2) and write –8 in it.
Th e calculation now looks like this:
(10 × 4) 8 × 37 =
–2
–3
–8